This paper presents results on the performance of 10 MW biomass-fired steam power plant. The main objective is to test the performance of the power plant using different type of biomass fuels: bagasse, corn stover, forest residues, and urban wood residues. The biomass fuel was mixed with sub-bituminous coal with fractions of 0–100%. The effect of excess combustion air, flue gas temperature, and the parasitic loads on the power plant performance was investigated. The output results from the heat and mass balance analysis include the monthly and annual electrical power generated, capacity factor (CF), boiler efficiency (BE), thermal efficiency, and gross and net heat rate. The results show a slightly decrease (1.7%) of the annual energy production when the biomass fractions increase from 6% to 100% but a substantial decrease of the CO2 equivalent emissions. A decrease of the excess combustion air from 25% to 5% will increase the boiler and thermal efficiencies and the annual energy output by 2%. This is mainly due to the reduction of the dry flue gas losses (DFGLs) with the reduction of the excess combustion air. A reduction of the parasitic loads from 10% to 2% will increase the power plant performance by 9%. This can be achieved by using more efficient pumps, fans, and conveyors in the power plant. A reduction of the flue gas temperature from 480 °F to 360 °F increases the power plant performance by 4.4% due to the reduction of the dry flue gas losses.